1. Field of the Invention
The invention relates to a photoresist composition and method of pattern forming using the same. More particularly, the present invention relates to a photoresist composition with multi-reaction systems and method of pattern forming using the same.
2. Description of the Related Art
With the progress of IC technologies, thin film photolithography has developed from G-line and I-line to deep UV and photoresist resolution processes have improved from 1 μm to less than 90 nm.
To conform to various electronics and optoelectronics requirements circuit board technology is evolving toward high density interconnection, fine pitch, and high aspect ratio. The thick film photolithography is the predominate process used in the above circuit board technology, and offers improved exposure by employing uniform ultraviolet (365 nm±10%) light as an exposure source.
The photoresist used in photolithography is usually dry film or liquid photoresist 10˜50 μm thick and with a 50 μm optimum resolution. Due to the multiple layer, and high distribution density requirements, the application of the present technology is limited. The circuit board requires a greater number of layers number to accommodate the longer circuit and the increased number of I/O points. Moreover, as electronic products become thinner and smaller, high density interconnection (HDI) substrates are the primary method of reducing manufacturing cost while maintaining the desired product size. Thus, photoresist resolution must be reduced to at least 10˜25 μm. Therefore, developing a simple photoresist technology offering a complete figure, high aspect ratio, and superior resolution is necessary.
Currently the optimum HDI resolution is 50 μm as disclosed in U.S. Pat. No. 3,953,309, 5,087,552, and 5,609,991. The conventional photoresist technology employs a negative mono-reaction type (free radical polymerization) photoresist using UV radiation to perform photolithography for a high density interconnection substrate.
When forming a high resolution photoresist pattern (with spacing width of less than 50 μm) using a conventional photoresist composition, the residual photoresist is difficult to remove and creates uneven surfaces due to defects such as distortion, swelling or raising, resulting from light scattering during exposure and the incomplete reaction of photoresist composition, hence, the photolithography resolution is limited.
The negative photoresist composition based on free-radical polymerization is highly reactive rate after exposure. The uniformity of reaction suffers, however, due to the occurrence of complex and uncontrollable side-reactions resulting from the high reactivity of free-radicals. Thus, photoresist defects, such as distortion, swelling and raising, frequently remain after high resolution photolithography.